Effect pigments, also known as nacreous pigments and pearlescent pigments, are lustrous specialty chemical products which are widely used in a variety of high-end applications such as automotive finishes. One of the attributes of the effect pigments is that they can generate a range of optical effects depending on the angle at which they are viewed.
In a number of applications, the effect materials have a lesser degree of hiding power than desired. One method which has been used to address this problem is to incorporate a carbonaceous material within the formulation. Users, however, would prefer that the carbon additive be supplied as a part of the effect material rather than separately to be added by the user prior to application.
Effect pigments are often based on platelet shaped particles. Because the optical effect is the result of multiple reflections and transmission of light, it is desirable to provide particles which will align in the medium in which they are found and to optimize the desired effect. The presence of either misaligned particles or particles of an additive, or both, interferes with this objective and diminishes the optical effect of the pigment. It is therefore desirable for the carbon additive being used for increased hiding to be somehow bound to the platelets rather than present as part of a physical mixture.
The formation of a carbon coating on a platy substrate is known. U.S. Pat. No. 3,107,173 discloses a coating of translucent micaceous flake substrates with a thin, adherent, substantially continuous, translucent layer of carbon. The carbon layer is formed on the flake substrates by pyrolyzing a carbon-containing material in contact with the flake substrate in an inert atmosphere.
U.S. Pat. No. 5,702,518 discloses a gold-colored pigment in which a substrate coated with metal oxides is characterized by a first layer of titanium dioxide doped with carbon obtained by thermal decomposition of organic colloidal particles and a second layer which is ferric oxide.
U.S. Pat. No. 5,356,471 teaches the formation of a platelet-like substrate coated with metal oxides in which a black surface color is achieved by reacting the platelet-like substrate with a silane followed by pyrolysis.
According to U.S. Pat. No. 5,286,291, prior art processes where carbon black was formed by pyrolysis of organic compounds or by mixing a substrate with carbon black followed by hydrolyzing a metal salt, results in producing pigments with insufficient wear resistance or the deposition of the carbon black on the pigment is in agglomerated form so that the pigments do not have good hiding power. To overcome this disadvantage, the patent teaches coating the platelet-like substrates with carbon black particles, and optionally a metal oxide, and being doped with an anionic or cationic and nonionic surfactants and an organosilane compound so as to fix the carbon black on the substrate and improve the abrasion and bleeding resistance of the pigment. The resulting product is calcined.
U.S. Pat. No. 5,271,771 teaches the formation of carbon-containing plate-like pigments by pyrolysis of carbon containing compounds in the presence of either plate-like metal oxides or metal oxide mixtures or substrates coated with titanium dioxide and at least one further metal oxide under conditions in which the metal of the metal oxide is reduced. The metal oxide or metal oxide mixtures can include Fe2O3.
U.S. Pat. No. 6,436,538 teaches effect pigments which are a collection of platelet-like particles coated with a nitrogen-doped carbon coating. This is made by adding a carbon and nitrogen containing polymer (or monomers to form the same) to the particles suspended in a liquid, coating the polymer on the surface of the particles, optionally in the presence of a surface modifier such as a neutral, cationic, anionic or amphoteric surfactant, reactive metal compound or polar polymer, and then pyrolyzing the particles in a gaseous atmosphere.
The object of the present invention is to provide a new process for forming carbon-containing, highly lustrous materials and to the resulting materials so produced. This and other objects of the invention will become apparent to those skilled in this art from the following detailed description.